A businessman has insisted Labour's chief fundraiser knew of his plans to give the party money using proxy donors and had said it was "a good idea".
Mr Abrahams' comments contradict the recollection of Jon Mendelsohn
In the Independent on Sunday, property developer David Abrahams repeats his claim that Jon Mendelsohn knew in April how he planned to make his donations.
Mr Mendelsohn said the allegations were "fictional" and that he only learned of the practice in September.
Gordon Brown has vowed to co-operate with a police probe into the affair.
The prime minister has also pledged to press ahead with an urgent review of party funding rules.
He told party supporters "immediate change" was needed in the party.
The prime minister told a meeting of Labour's ruling national executive committee that recent events showed it was "time to act".
He has previously said the donations were "completely unacceptable" and would be re-paid.
Mr Brown appeared alongside deputy Labour leader Harriet Harman, who was drawn into the donations row when it emerged she had accepted a £5,000 donation from one of Mr Abrahams's proxies.
Ms Harman - who insists she acted in good faith - admitted it had been a "very painful week for the party".
In his article, Mr Abrahams describes being placed next to Mr Mendelsohn at a London dinner in April this year, which he believed at the time was "just a little more than coincidence".
Mr Abrahams said he understood at the time that Mr Mendelsohn was hoping to become Labour's chief party fundraiser.
"He did not solicit funds from me at the dinner," Mr Abrahams continues.
"However, I told him that I regularly donated to the party and I described how it was done through intermediaries for the purposes of anonymity - to which he replied, 'That sounds like a good idea'."
Mr Abrahams has donated more than £630,000 to the Labour Party since 2003 - but donated under the names of third parties.
By law, anyone donating more than £5,000 must be identified and relevant details about them disclosed.
In a separate statement, David Abrahams urges Mr Mendelsohn to "stop damaging himself and the party's credibility".
"I will not stand by and allow my name to be put in the frame by spin doctors," he continues.
"The police must be allowed to conduct this enquiry free from the interference of politicians.
"For my part, I refute any wrongdoing and I am confident of my legal ground."
Mr Mendelsohn said in a statement he would co-operate fully with the police investigation.